This invention relates to a method and means for detecting whether or not the wheels of a freight car are too slippery for the car to be adequately retarded by retarders while being rolled to a location where it will couple with other freight cars.
In gravity classification yards, a freight car is pushed by a locomotive to the top of a small hill, called a hump, and then is allowed to roll down under the influence of gravity. There are a large number of branching tracks from the track which runs down the hump and the freight car is directed into one of these branches as determined by the location of a freight train which is being made up and which will be going to the destination of the cargo in the particular freight car.
The velocity which the freight car attains, coming down the hump, must be controlled. If it is too small, the freight car will not be able to reach the location of the partially made up freight train. If it is too large, the freight car will smash into the partially made up freight train, thereby causing damage either to the freight car or to the cargo which it carries.
Retardation of freight cars in gravity classification yards is dependent upon the proper frictional coefficient produced by contact between the retarder shoes which are in the retarders which are used to control the freight car velocity, and the sides of the wheel flanges on a car being retarded. If any foreign matter accumulates on the wheels flanges or the retarder shoes, which effecitvely decreases the frictional coefficient, the possibility of an inadequate retarding effect is presented.
In order to prevent crashes of the type described, a device is required which can determine whether or not the wheels of a freight car or the retarder shoes are so slippery that the car will not be adequately retarded, prior to the freight car being pushed over the hump of a gravity classification yard. Such a device could certainly reduce the number of expensive crashes.